Pneumatic tube and method of manufacture



Dec. 8, 1931. w. c. MARTIN PNEUMATIC TUBE AND METHOD OF MANUFACTURE Filed May 31, 1929 Z@Q 1///////////////n- Patented Dec. 8, 1931 UNITED A STATE-S. PATENT OFFICE WILLIAI 0. mm, 01? OBICAGQ, ELI N018, ABSIGNOB T JOHN 3'. LEE, 01 OAK PARK,

ILLINOIS rimuua'rrc me am) men or nnurac'rm Application fled Kay :1. 1029. Serial m. scam.

This invention relates particularly to the manufacture of an improved uncture-proof tube for pneumatic tires, and t e primary ob ject is to provide for the production of an im- 5 proved tube of this character by an improved method which will insure the reservation of the self-healing quality of t e tube and at the same time enable such tubes to be manufactured rapidly and economically. w The invention is illustrated in a referred embodiment in the accompanying rawings,

. in which Figs. 1-4 show the several component parts enterin into the structure of the tube; Fig. 5, a bro en'sectional view illustrating the manner in which the parts of the tube are built up on a mandrel or drum; Fig. 6, a broken sectional view illustratin the manner in which the tube is molded an vulcanized;

and Fig. 7 a view showing a modification of the element shown in Fig. 2.

The invention contemplates, in the preferred practice of the process, the pro 110- tion of the tube as a whole by a single vul- 25. canizing operation, suitable recautions being taken to preserve the se f-healing compound which is em loyed from bein vulcanized, or hardene by preventing t e migration of sulphur into said compound during the vulcanizing operation.

Referrin to Figs. 1-6, A designates a strip of rugber which is formed into a tube; Y B a strip of rubber which serves as a treadthickening pad; C a strip of self-healing compound having an enveloping and protecting jacket 0' and D a relatively narrow strip of rubber between which and the tube-forming strip A the bodies B and C are confined. w The strips A, B and D are of uncured rubber, suitably compounded with sufficient sulphur to enable them to be properly cured in accordance with-the usual practice of ouring inner tubes, but avoiding-the presence of free sulphur after the operation. The strip B has a thickenedcenter. portion and tapering edge portions. a

The strip C is composed of a self-healin compound, which is not supplied with su phur, and which is, in the process of manufacture,.protected against sulphur reaching the same by) migration. The self-healing body C may e composed of any suitable comound which will serve the purpose. The ollowing is a suitable compound Pounds Ounces Rubber Ereolalmed) Rubber rolled brown crepe) Synthetic so-called llqul rubber Granule asphaltum or mineral rubber (M. R. X.) Neutral lubricating oil is known on the market as Junior Red Engine Oil. The so-called mineral rubber may be a pine tar composition, an asphalturn composition, or a mixture.

The ingredients of the self-healing compound may be mixed on the rolls or 1n any suitable manner. The material may then be rolled into sheets; these sheets ma be cut into strips of varying widths; and t e strips which are of somewhat soft, tacky character, may be ressed and formed to provide a thickene center portion and tapering edge portion. Another and more rapld method is so extrude the composition through a suitable The stri .B may also be extruded through asuitable ie? The envelope 0 which protects the selfhealing compound from vulcanization, may consist of a cured rubber strip, or a semicured rubber strip. The strip may be folded about the compound in the manner illustrated in Fig. 2. If desired, paper impreg- I may be composed as follows Lbs.

Rubber 100 .Litharge 20 Zinc oxide 5 Sulphur 3 The sulphur is used in such limited amount as to effect a suitable cure of the compound. It will not pass, however, into the self-healing com ound owing to the greater afiinity of the litharge or lead oxide, for sulphur. Under suitable conditions, it is possible that the sulphur may be omitted from the coating, designated C, shown in Fig. 7.

In forming the tube in accordance with the preferred method, the strip A is first wrapped about the drum E and the ends broug into overlapping relation; the strip B is then wrapped about the drum and its ends brought into overlapping relation; the strip C within the envelope C is then wrapped about the drum and its ends brought into overlapping relation; the strip D is then wrapped about the drum and its ends brought into overlapping relation. The joints at the ends of the strips may be broken if desired. The strips B and C may have their ends ta red at the overlaps. Finally, the lateral e (ge portions of the strip A are curved upwar ly and brought into overlapped relation in the manner illustrated by the dotted lines in Fig. 5.

The tube is then placed in a vulcanizing full-circular mold G; heavy air pressure is introduced; and steam is admitted to the mold to effect the curing operation. The ourin may be completed within a few minutes.

t will be noted that the manner in which the tube is formed in Fig. 5 results in reversing the order of the pad B, the self-healing body 0, and the covering strip D. Thus, the pad B is, after the curing operation, outside of the self-healing body. In the curing operation, the tube A, pad B, and strip D unite and become a practically integral formation; and the self-healing body C is contained within the thickened tread-portion of the tube. The pad B coalesces with the tread-portion of the tube A, and thus a thick cured tread-portion of rubber is formed outside the self-healing. body. In case of a puncture, followed by withdrawal of the puncturing nail, for example, the self-healing compound adheres to the surface of the nail and is drawn therewith into the puncture opening, effectively plugging the opening.

Repeated demonstrations under practical working conditions have proven that a tube of this character may be punctured hundreds of times without appreciable loss of pressure.

It is highly important that the tread-portion of the tube should be composed of thickened, vulcanized rubber; and it is also highly important that the self-healing compound be sufficiently mobile and tacky to flow into and close the puncture, without being in liquid condition. Also, it is important that the compound shall be of non-freezing character, and that it shall be so protected that vulcanization cannot occur under the effect of heat developed by the use of the tire in hot weather. By preventing sulphur from reaching the selfealing compound, injurious change of the composition is prevented, even though the tire be subjected to working conditions producing a high temperature.

In my application, Serial No. 311,303 filed October 9, 1928, I disclosed a method of producing a puncture proof tube. In that case, migration of sulphur into the self-healing compound was prevented by employing a prevulcanized inner tube and a pre-vulcamzed pad, the self-healing compound being introduced between the pad and inner tube in the process of manufacture. The product produced by the process referred to is highly efi'ective as a puncture proof tube, but is expensive to manufacture. The present process greatly reduces the cost of manufacture and enables a large output to be obtained in a factory of moderate size and limited equipment.

It may be added that in building up the tube in the manner illustrated in Fig. 5, the uncured rubber sheets will readily adhere together when treated slightly with gasoline at the surfaces which are to be stuck together. The sheets may be stuck together by slight compression, such as can be produced by a small tool or wheel by the well known stitching operation.

If desired, the protecting compound C may be applied to adjacent surfaces of the strips B and D (Figs. 1 and 3), thus serving as a substitute for the jacket C, which may in that case be omitted. Also, if desired, the strips A and B, instead of being produced separately in the first instance, may be produced as one piece. Other modifications are contemplated.

It may be added that where the pad B is se arately formed, it may be of a cheaper ru ber compound than is desirable in the tube-stock of the sheet A. In ractice, the envelo e C which may be very tl iin coalesces with t e pad B and the strip D in the vulcanizing operation.

It will be noted from Fi 6 that the tubeforming sheet A is provided, prior to the vulcanizing operation, with a valve-stem G which enables the tube' to be inflated after the mold has been closed.

rubber (pure, uncompounded gum) is vul- The green rubber tube having a thick treadportion provided with a circumferential cavity containing a sealin compound effectively protected against sulp ur migration may be built up in any suitable manner; and such a structure may be vulcanized as a unit without destroying the self-healing quality of the self-healing plastic described. That is, while the plastic described is capable of vulcanizution, it is effectively protected against vulcanization. It may be remarked that raw canizable and will not, alone, serve to revent vulcanization; hence, it is not suitab e for a protecting envelope, even thou h it contains no sulphur, owing to the fact t at migration of sulphur will occur from the adJoining compound containing sulphur.-

T e foregoing detailed description has been given for clearness of understanding only, and no unnecessary limitations should be understood therefrom, but the appended claims should be construed as broadly as permissible in view of the prior art. I What I regard as new, and desire to secure by Letters Patent, is;

l. The method of producing a punctureproof inner tube, which comprises: formin a tube of vulcanizable rubber compound, sai tube having a thickened tread-portion containing therein a body of self-healing compound protected against sulphur migration;

and vulcanizing said tube.

2. The method of producing a punctureproof inner tube, which comprises: formin a tube of vulcanizable rubber compound, sai tube having a thickened tread-portion containing therein a body of self-healing compound protected against sul hur migration; and introducin said tube into a mold and inflating and vu canizing the tube.

3. The method described in claim 1, characterized by the use of a protecting envel about the body of self-healing com ound e fective to prevent vulcanization o the selfhealing compound.

4, The method described in claim 1, characterized by the use of a cured or semi-cured rubber envelop enclosing the body of selfhealir ig1 compound.

5. e method specified in claim 1, characterized by the use of aprotecting envelop about the body of self-healmg compound, containin g a chemical agent havinga high aflinity for sulphur.

6. The method of producing a punctureproof inner tube, which comprises: building upon a mandrel a carcass comprising a tubeforming strip, a tread-thickening strip, a sheathed strip of self-healing compound, and a relatively narrow housing strip; bringing togetherthe lateral edges of the tube-formstrip; and inflating and vulcanizing the within a mold.

7. The method of producing a puncture- 

